Thermostatically operated valves are used in vehicle engines in which they move between an unactuated position and an actuated position to control the flow of a fluid such as water or oil through a cooler, for example, a radiator, in response to the temperature of the fluid. These valves have been known to fail, so that they remain in their unactuated positions. The failure of such valves in such a position has resulted in significant overheating of the water or oil and severe damage to the engine.
In response to the problem of thermostatic valve failure, fail-safe devices have been designed which include safety provisions in case the valve fails to operate in its principal mode as intended. For example, U.S. Pat. No. 3,045,918 to Woods discloses an actuator in which a valve element is biased to the closed position by a spring in tension. Furthermore, one embodiment of the actuator is disclosed in which a predetermined temperature above the range of normal operating temperatures of the valve causes the softening of material which anchors the spring to the valve element, thereby allowing the valve element to fall away from the valve seat. U.S. Pat. No. 3,498,537 to Wong discloses a fail-safe thermostatic valve which is mounted in a flow path by means of an annular connector member of fusible material which melts or softens at a temperature above the normal operating temperature, so that the pressure of the fluid moves the valve out of its mounting and permits the flow of fluid around the valve. U.S. Pat. No. 3,776,457 to Cardi discloses a thermostatic valve mounted in parallel with a heat softenable plug, so that if the valve fails to open, the plug will soften and open in response to a temperature above the temperature for which the thermostatic valve is designed, whereby a flow of the controlled fluid bypasses the valve.
Although the foregoing prior devices disclose the concept of fail-safe arrangements, the Cardi device, for example, requires a thin-wall support structure in order to mount the plug in parallel with the valve. In addition, none of the devices mentioned includes a mechanism for positively clearing an opening through which the fluid can flow when the valve operates in the fail-safe mode.